Retrieving Dialed Phone Numbers from Intercepted Phone Calls

Over on his YouTube channel Linux Psycho has uploaded a video showing how he was able to listen in on wireless phone calls and recover the dialed phone numbers from within the conversation. 

The intercepted signal appears to be unencrypted in the clear NFM at 130 MHz and appears to originate from some sort of wireless telephone service. Heard in the phone call are DTMF dial tones. Later in the video Linux Psycho shows how to retrieve the dialed phone number by recording the DTMF tones and submitting the .wav file to an online DTMF tone detection website. DTMF tones are simply the tones that you hear when you dial a number on a landline phone. Each tone is a different frequency and so it is fairly trivial to recover the dialed numbers.

We’re not sure exactly what the signal that Linux Psycho is listening to actually is as it seems to be a cordless phone, but in the wrong frequency range. Potentially it is a long range wireless phone extension commonly used in the third world or rural areas where actual landline connections are rare.

rtl sdr new, rtl sdr phone hacking

8 comments

    • Linux Psycho Team

      Well I am not sure, I am still scrutinizing the origins!

      By the way thanks for informative pdf. I will go through and shall update if any further findings…

      Linux Psycho Team

  1. GetItRight

    Linux Psycho appears to fail to notice 130mhz is in the aviation band..amateur use not permitted…aircraft only….This could be a phone patch to airline companies!!

    • Linux Psycho Team

      @GetItRight, you are absolutely right. But, that’s what I discovered a strange frequency shuffling and I shared to you guys. That’s also strange indeed for me as even cordless phones are also not permitted in that particular frequency. The calls are individuals not govt or someting.

      Regards,

      Linux Psycho Team

  2. GiamMa-based researchers SDR R&D IoT

    Hello,

    To better understand what has been decoded, I would like to ask you if you are sure to decode phone numbers?

    In the 130Mhz band, many amateur radio and professional radios use DTMFs as service codes.

    If you wanted to decode in real time and offline the DTMFs with an SDR and an android device, just download one of the many DTMF Audio Decoding apps and an SDR management app.

    Set the listening frequency with the SDR management app where the DTMF codes are transmitted via radio, open the DTMF Audio Decoding app and wait for the decoding. (If I have time I will try to generate a video to show this idea)

    • Linux Psycho Team

      Yes the phone numbers were decoded successfully. There are lot of apps for smartphones to decode the DTMF tones. But I used dialabc.com because it can decode the fast lapsed tones easily and till now I didn’t experienced any other source for decoding as accurate as dialabc.com.

      Regards,

      Linux Psycho Team

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